Nitrogen levels have got worse in more than half the rivers monitored by environment officials, a new report shows.
In the report, released this morning, the Ministry for the Environment says freshwater is coming under increasing pressure from agricultural and urban areas.
Our Fresh Water 2017 is the first dedicated report on freshwater since the ministry was legally required to produce them in 2015. It will become a benchmark for tracking the change in freshwater quality over time.
Read the report here.
The report measures the quality of waterways, water quantity and flows, biodiversity in rivers and lakes, and the cultural health of fresh water.
New Zealand was fortunate to have plenty of fresh water, the report said.
"But like the rest of the world, it is becoming increasingly clear our natural resources are limited if we continue to use them in the same way we have done."
The report's starkest findings were those about nutrient levels in waterways.
Nitrogen levels were getting worse at 55 percent of monitored river sites across New Zealand and getting better at only 28 percent of sites, the report said.
Phosphorus levels were getting better at 42 percent of monitored river sites and getting worse at 25 percent.
Nitrogen and phosphorus are the nutrients of most concern in New Zealand's freshwater because high concentrations can cause excessive plant growth and algal blooms.
That reduced oxygen levels and prevented light from penetrating the water - affecting freshwater plants and animal species.
Very high concentrations of nitrogen can be toxic to freshwater life and can make water unsafe for people to drink.
The report also reviewed E coli concentrations in water, but found there was insufficient data to determine trends the bacteria between 2004 and 2013.
However, it found E coli concentration was 22 times higher in urban areas and 9.5 times higher in agricultural areas, compared with land covered by native vegetation.
Agricultural land covers about half of New Zealand. The report said the country has one of the world's highest rates of agricultural land intensification over recent decades.
Dairy herd numbers increased nationally by 69 percent between 1994 and 2015, to 6.5 million.
And in the Canterbury, Southland and Nelson regions, dairy cattle numbers rose six-fold in the two decades between 1994 and 2015.
Pressure on fresh water from agricultural practices include increased use of fertiliser; urine and faeces from livestock; irrigation; accelerated erosion from forestry, livestock, and cultivated soils; and infrastructure development.
Dairy cattle numbers by region: 1994-2015
The report estimated that nitrogen leaching from agricultural soils increased by 29 percent between 1990 to 2012, because of increased urine and faeces from livestock and fertiliser application.
Urban activities were also affecting water quality, it said.
While urban land only covered about one percent of New Zealand, 87 percent of people live in urban areas, and the population grew 17 percent between 1996 and 2013.
Streams in urban areas were prone to rapid changes in flow, elevated concentrations of nutrients, highly modified channels and reduced biodiversity, the report said.
They also suffered from increased bank erosion and the water carried a high amount of sediment downstream.
Both rural and urban activity had an effect on biodiversity, the report said.
"Of the native species we report on, around three-quarters of fish, one-third of invertebrates, and one-third of plants are threatened with, or at risk of, extinction."
Seven species had a decline in conservation status between 2005 and 2013, it said.
Three other species - including the longfin eel - had decreased in abundance.
Water quantity and flows
The report said while New Zealand has plenty of freshwater, it is not always where it is required and when the flows of rivers are reduced, algae and fine sediment could build up.
It also had an incomplete picture of some water use.
"More than half the water consents granted by councils are for irrigation, but we do not know how much of this is actually used," the report said.
"In future reports we aim to provide a more complete national picture of how much water is actually used."
Canterbury accounted for 64 percent of the total consented volume of water for irrigation, the report said.
Human demand for water had resulted some of the country's waterways being physically altered through diversions from one waterway to another, dams and bores.
Data gaps hinder report
The report concluded that there were major data gaps that prevented it from making clear findings in many areas.
The gaps included:
- How much water was actually being used and how that was affecting flows, water availability, and habitats
- The amount of sediment deposition
- The national abundance and distribution of many native species
- The health of wetlands and recent changes in their extent
"Some of this information is being gathered now, such as recording freshwater takes," it said.
"The next steps for this programme are to work with others to prioritise and determine how we start to fill these, and other, important gaps that may arise."